Plumbates such as red lead, lead suboxide, lead cyanamide, calcium plumbate or basic lead sulfate, and chromates such as basic potassium zinc chromate, tetrabasic zinc chromate, barium chromate, calcium chromate or strontium chromate have mainly been us ed as an anti-corrosive pigment. Nevertheless, although these anti-corrosive pigments exhibit excellent rust-prevention performance with metals, their use is being restricted in view of health and environmental protection problems.
As non-pollution type anti-corrosive pigments to be used in place of those pigments, non-pollution and harmless anti-corrosive pigments such as phosphates such as zinc phosphate, magnesium calcium phosphate, titanium phosphate or silica phosphate; condensed phosphates such as aluminum triphosphate; phosphites such as zinc phosphite, calcium phosphite, strontium phosphite or aluminum phosphite; zinc molybdate; calcium molybdate; barium borate; zinc borate, and the like, have been developed, and are being partially put into practical use.
However, since these are not comparable to the chromic salt-type or plumbate-type pigments, pigments having stronger rust-prevention are demanded. There has been proposed, for example, non-pollution-type white anti-corrosive pigments, such as basic zinc phosphite (Japanese Patent Laid-open No. Sho 50-50297), zinc hydroxyphosphite complex (Japanese Patent Laid-open No. Sho 58-194725), an anti-corrosive pigment by the reaction product of zinc phosphite and zinc white (Japanese Patent Laid-open No. Sho 57-109862), an anti-corrosive pigment of potassium zinc phosphite-type (Japanese Patent Laid-open No. Sho 58-84109, Japanese Patent Laid-open No. Sho 59-20466), calcium zinc phosphite-type (Japanese Patent Laid-open No. Hei 3-111457), plate-like calcium phosphite-type (Japanese Patent Laid-open No. Hei 3-285808), an anti-corrosive pigment obtained by chemically modifying the surface of condensed phosphate and zinc compound and/or borate compound (Japanse Patent Laid-open No. Hei 2-151664), an anti-corrosive pigment in which an organophosphorus compound having a chelate ability is contained in zinc phosphite and/or calcium phosphite (Japanse Patent Application Laid-open No. Hei 6-93478), an anti-corrosive pigment comprising an anti-corrosive pigment obtained by reaction treating zinc oxide with an organophosphoric acid having a chelate ability, and a mixture of this anti-corrosive pigment and a white anti-corrosive pigment of phosphate-type or phosphite-type (Japanese Patent Laid-open No. Hei 6-122986) and the like.
Although the above-mentioned non-pollution-type anti-corrosive pigments may be expected to have an effect to a certain extent, and although, non-pollution-type anti-corrosive pigments for electro-deposition coatings and coil coating system used in coating automobiles, electric appliances and the like are particularly urgently needed, one that is comparable with plumbates or chromates has not yet been put into practical use.
On the other hand, with regard to coatings containing these anti-corrosive pigments, substitution to water base coating from the conventional solvent-type coating is being requested from the stand point of environmental problems, and the development of non-pollution-type rust-preventive coating exhibiting more effective rust-prevention is desired.
As the result of extensive research on non-pollution type anti-corrosive pigments in view of the above-mentioned circumstances, the present inventors have found that an anti-corrosive pigment composition containing, as main components, white anti-corrosive pigment and inorganic anion exchanger carrying NO.sub.2.sup.-, NO.sub.3.sup.- or MoO.sub.4.sup.2- has excellent rust-prevention and shows stable pigment characteristics, and completed the present invention.